According to California Business and Professions Codes 2395 and 2396, physicians responding to emergencies on a volunteer basis to care for people who are not their patients are generally protected from liability. The same holds true for physicians volunteering at school athletic events. This isn't a substitute for malpractice insurance, however. You could be sued and need to defend yourself, though the law is likely to be on your side. For more information on this issue you should contact your malpractice carrier or go to The CMA Website
and download CMA On-Call document number 0820, Good Samaritan and Other Immunities.